In semiconductor device production, and in particular in the production of solar cells, doped sections are produced on a semiconductor substrate by means of doping or deposition, said doped sections forming with the substrate material, depending on the purpose of application, a pn junction, a pp+ junction or an nn+ junction. In the case of photovoltaic elements such as solar cells, for example, a pn junction can serve for separating free charge carriers generated upon the incidence of light. By contrast, pp+ junctions or nn+ junctions are so-called high-low junctions which, arranged below a metal contact, allow improved contacting of the semiconductor device, and, secondly, can also lead to a reduced recombination activity and thus to a higher efficiency of the semiconductor device.
Such junctions can be produced on the front and/or rear side of the semiconductor device. By way of example, they can be formed by means of locally doped sections, in particular by means of locally highly doped sections, as is the case for example for so-called selective emitters. Such local dopings are usually introduced with the aid of laser-induced diffusion processes. One example thereof is constituted by, inter alia, the alloying of aluminum from a metal layer into an underlying semiconductor substrate by means of point-type laser irradiation. This alloying process also proceeds during the laser-induced contacting of an aluminium film with a semiconductor substrate, the result of which is designated as a laser-fired contact (LFC).
Further known processes for producing local dopings are local diffusion from a diffusion source applied locally to the semiconductor substrate or local diffusion through a diffusion mask. However, such processes are generally complex and expensive, either since they require expensive diffusion sources or because the masking is complex. Moreover, the process windows for such processes are often small. Furthermore, there is often the problem that, after the doping step, a further functional layer has to be applied on the doped semiconductor substrate, for example a passivating layer or a reflection or antireflection layer. In order then to be able to contact the doped sections, contact openings have to produced through the functional layer, said contact openings being aligned exactly with the doped regions.